Casting screw threads on blast nozzles and the like



May 23, 1950 D. C. TURNBULL CASTING SCREW THREADS ON BLAST NOZZLES AND THE LIKE 3 Sheets-Sheet 2 Filed Feb. 9, 1946 m l 1 1 a INVENTOR. 04 W0 C. TUPNBULL BY MTLLJMWQ-MQM A T TOQ/VEYS May 23, 1950 D. c. TURNBULL CASTING SCREW THREADS ON BLAST NOZZLES AND THE LIKE 3 Sheets-Sheet 3 Filed Feb. 9, 1946 Patented May 23, 1950 CASTING SCREW THREADS ON BLAST NOZZLESAND'THE LIKE David. G. Turnbull, Mishawaka, Ind, assignorto American Wheelabrator & Equipment Corporation, a corporation of Delaware Application February 9, 1946, Serial No. 646,532

.2 Claims.

The invention relatesto blastnozzles such. as used for directing a stream. of compressed air carrying sand or other 'a-brasive.

Such blast nozzles usually comprise a body or fitting connected to the rubber hose and a nozzle casing screw threadedto the fitting. The nozzle casing usually has aliner of suitable wear-resisting material secured therein. These'fittings and casings are subject to considerable wear from rebounding abrasiveand hence are made of hard metal. In 'thejpast, such fittings and casings have been made by machining,.then cutting the threads and then heat'treating to obtain the desired hard wear resisting surface.

It is proposed, according to the present invention, to cast screw threaded casings and fittings of hard non-machinable metal with thefine pitch, sharp corner, machine screw threads :cast direct and thus eliminate the need for machining, heat treating, etc. and, at the same time-obtain greatly increased life.

It is preferred that thescrew threaded product be formed by a special threaded core member which is placed in the mold. Suchcore member may be formed in difierent Waysdependi'ng upon the shape of the final product. For making the nozzle part used to illustrate the invention, a metal core box is provided comprising a cupshaped receptacle having ascrew threadedspindle or ram adjustably threading into the cupshaped mold space. A mold plate closes themold space. The mold spaceisfilled with core sand and the screw threaded ram forced through the sand to make the thread impression, the sand "being extruded through an opening in themold plate. The ram is then withdrawn. Theturning of the screw threaded member into the moldable material and then withdrawing by reverse turning, packs and smooths the threaded mold surfaces, making an accurate surface for the fine pitch, sharp corner screw threads. The annular internally threaded core is then removed and baked.

According to apreferred methodof molding the nozzle part illustrated, a metal pattern member having, integral core prints is first molded into the molding'sand after which the pattern'is removed and replaced by the annular threaded core above described and an inner core.

The invention is applicable to forming internal screw'threa'ds as'well as externalscrew'threads.

The'invention also consists in certain new and original features and combinations hereinafter setfortnand'claimed.

'Althoughthe 'novelifeatures" which are believed to be characteristic of thisinvention-willbe par, ticularly pointed out in the claims. appended hereto, the invention itself, as to its objects and advantages, and the manner in which itm-ay :be carriedout, may be better understood by referring to the following description taken in connection with the accompanying, drawings. forming'a part hereof, in which:

Fig.1 represents one .form otnozzleswhich may be made according to the invention;

Fig. 2 is an end view. ofthe nozzle;

Fig. 3 represents a detail of the nozzle casing, used .to illustrate the preferred methodandiappat ratus forcarrying out this method;

Fig. 4' illustrates one type of metal .corebox which may be ;used for molding a screw threaded core;

Fig. 5 illustrates the same .core box as Fig. 4 but showing another. step in the process;

Fig. 26 illustrates a molded screw threaded core according to theinvention;

Fig. -'7 is a section through a foundry mold illustrating a step in the process and showing positioningof metal patternandnore printintem 'nal core, runners and sprue pin;

Fig. 8 illustrates. asucceeding stepintthe process showing a single moldsectlon with metal pattern, core print :and' "runners. removed and with the annularicore' inzplace;

Fig. 9 illustrates a further stepiln thennoldlng process with the mold sections together andawith the inner core inplaoe; :and

Fig. 10 illustrates diagrammatically the rela. tionship of the finished 'productafter it is poured with respect-to the-other parts of the mold.

'In the following description and in the claims, various details will b'e identified by specific names forconvenience, but they are intended to be as generic in their application as the ar-t' will' permit.

Like reference characters denote like--parts1n 'theseveral figures of the=drawings.

invention.

Referring now to the drawings and --mor e par- "ticularly to "Figs. 1 to "3, the nozzle assembly,

shown for purposes of illustration, comprises a nozzle body or fitting I 0' screw threaded to the nozzle casing H whichcontainsthe hardinsert J2 held "in position by cement 16. The nozzle body "I'll issecure'd to-rubber hose 1-5 as *bywood 3 screws Hi and a flaring hard metal nipple I4 engages rubber hose l5 and a rubber gasket l3 to direct smoothly the mixture of fluid carrier and solid abrasive particles into the nozzle opening. The insert [2 may be made of suitable wear resisting material such as ceramic, tungsten, boron, etc. This material is very hard and wear resisting but is brittle so must be protected by the surrounding metal case.

The nozzle casing H has screw threads I! and the nozzle body ID has screw threads l8. These parts are readily detachable so that they may be replaced when worn. The outer metal parts Ill and l are made of a hard hollow wear-resisting metal having a hardness of around 55 to 65 Rockwell C which is so hard that it cannot be filed or machined, is very diflicult and costly to grind and therefore highly resistant to wear. The screw threads l1, l8 are formed into their respective parts during the casting operation as will be explained hereinafter.

Although the screw threads ll, l8 shown for purposes of illustration, are of the V-type and straight, other forms of screw threads both straight and tapered, such as for example as commonly found on pipes and bolts, may be formed according to the invention. The screw threads may vary in size from eighteen threads to the inch to four or less threads per inch.

The nozzle casing H has a polygonal wrench engaging portion 19 and an annular clearance groove 38 at the junction of smooth inner bore 31 and shoulder 55. Outer surface 55 is tapered.

Referring now to Figs. 4 to 6, for purposes of illustration a core box will be described for molding a threaded annular sand core to be used in molding the screw threaded nozzle casing I above described. This core box is for the purpose of making the mold core ring 33 illustrated in Fig. 6. This mold core 33 has internal screw threads l'la molded therein which act as the mold to form the screw threads ll on the nozzle casing H as described hereinafter. The core 33 has the usual conical surface 34 to assist in placing in, and withdrawing from, the mold, as will be understood by those skilled in the art.

The apparatus for making the mold core 33 comprises a metal mold plate 2|) having a shallow recess 2|, a central extrusion opening 22 and a plurality of legs 23 adapted to rest on a bench or other suitable support, as shown in Fig. 5. The box 36 comprises a cylindrical section 24 having a cup 25 containing a tapered mold cavity 26 for forming the core 33. The box has an end flange 21 and a stepped outer surface 90.

The cylinder 24 also contains a brass bushing 28 screw threaded internally except for a relieved portion 35. These screw threads are engaged by a screw threaded ram member 29 having a flanged top 3!! with radial capstan holes 3|. The ram 29 is made hollow for lightness and to facilitate heat treatment; it has a stopper 32 in its lower end to provide a smooth solid face to work against the core material. The threaded ram 29 may be of steel with its threads accurately cut and polished smooth, and hardened, since it is these threads that cut the threads into the finished core 33. There must be no backlash between the ram threads and the bushing threads or else the mold threads will be imperfect and not have sharp corners.

To use the core mold to form the baked core 33, the core box rests, inverted, with its top flange 30 on a work bench or other suitable support with the ram 29 withdrawn so as to make its surface flush with the bottom of the recess 26, as

shown in Fig. 4. The recess 26 is then filled with core sand which is patted down and struck off level with the outer edges of the cup 25. The mold plate 20 is then placed inverted over the top of the box with the cup 25 disposed in the shallow recess 2|. The entire assembly is then inverted and placed right side up on legs 23 on the bench support in a position indicated in Fig. 5.

The ram 29 is then turned downwardly, using pins (not shown) in the capstan holes 3| if desired to facilitate turning the screw. This turning forces the sand down and to the sides of the cup, filling the threads of the ram 29 and packing the sand uniformly on all surfaces. The surplus sand is forced out through the hole 22 in the mold plate 20 as the ram is turned home against the surface of the plate 20. The ram 29 is then turned back to its starting position, this action further compressing and smoothing the thread surfaces impressed or cut in the sand. The size of the opening through which the sand is extruded must be such as to cause the correct pressure to be built up in the sand by turning the screw.

The assembly is again inverted to rest on the flanged top 30, the mold plate 20 lifted off; a thin flat plate (not shown) is laid over the box 36 and the box again turned over. The box 36 is then lifted off leaving the core 33 on the thin plate where it can be handled without damage. The tapered surface 34 facilitates separation of box and core. The core 33 is then placed in a core oven to bake and harden.

If desired, a suitable clamping device (not shown) may engage the mold plate 2|] and one of the steps 60 on the box to hold the parts of the mold together.

Referring now to Figs. 7 to 10, one manner of preparing the mold for casting a nozzle casing II will be described, although it will be understood that the principles disclosed herein may be used for casting other shapes and with different molding apparatus.

In the method illustrated in Figs. 7 to 10, a special metal mold plate 42 is used with a drag 4t and a cope 4|. The special mold plate 42 has a central opening 50 for a sprue pin 5|, about which are a plurality of holes 54 to receive a plurality of inner cores 48, one of which is indicated. 7

This apparatus may be used as follows. Mold plate 42 is placed on a bench. The plurality of metal patterns 43 may be permanently fastened on the mold plate 42 centered over the core holes 54. The patterns 43 make the impressions for polygonal portions I9 and tapered barrel 56 of the finished nozzle casing H and also carry annular core print portions 39 for thread core 33 and tip print portions 46 for a purpose hereinafter explained. The patterns 43 also have end recesses 5'! for projections 41 on the inner cores 48 and annular recesses for projections 45 on the inner cores 48. The metal runners 44 may be permanently fastened on the mold plate 42 connecting the patterns 43 with the sprue pin hole 5|].

Drag 40 is then placed on mold plate 42. Sand 53 is then packed into the drag 40 around patterns 43 and runners 44 and leveled off on the top to obtain the relationship shown in full lines in Fig. 7.

A mold plate (not shown) is then placed on drag 40, which drag 45 with the last mentioned 76 top plate and bottom mold plate 42 is turned over. The center cores 48, together with sprue pin 5|, are placed in position in their various holes in the mold plate 42. Cope 4| is then placed on mold plate 42 and molding sand 52 packed into the cope 4| around sprue pin 5| and the flaring ends of cores 48. The relationship of the cope 4|, inner cores 48 and sprue pin with respect to the drag 40 is as indicated in Fig. 7.

The projections 41 on the center cores 48 are centered in corresponding recesses 5! in patterns 43 and the flask parts 40, 4|, 42 are held from swaying by the usual guide pin and holes (not shown) on the sides of the cope, drag and mold plate as will be understood by those skilled in the art. There is a slight clearance between the sides of the patterns 43 and center cores 48 to take care of any slight swaying.

The sprue pin 5| is removed and the cope 4| is then lifted off mold board 42, with the center cores 48 anchored in the sand 52, and set on a cradle (not shown) with the cores hanging vertical. Sprue hole 5|a is flared as indicated in Fig. 9. Mold plate 42, nozzle patterns 43 and runners 44 are then carefully lifted from the sand 53 in drag 40 after which the baked thread cores 33 are placed in the mold recesses left by the core print portions 39. The mold will then have the appearance shown in Fig. 8 which illustrates the ducts made by the runners 44 and the mold openings made by the patterns 43.

The cope 4| still carrying its mold sand 52 and inner cores 48 is then replaced on the drag 49 in the position shown in Fig. 9, the several inner cores 48 taking their proper positions within the several outer cores 33 and the mold recesses for the fittings I. It will be noted that the projections 41 on the inner cores 48 fit into shallow recesses 46a formed by corresponding core prints 46 on the patterns 43, the distance between the bottom of pattern recesses 51 and core prints 46 being equal to the thickness of special mold plate 42.

The mold is now ready for pouring. The molten extra hard alloy is then poured into the central gate 5|a where it runs through the runner ducts into the mold spaces, filling the entire mold and forming the molded product Attention is called to Fig. which shows the relation of the molded product to the outer core 33 and inner core 48. The lips formed by the runner ducts and any fins are then broken and ground ofi, to form the finished products Similar patterns, similar core box and similar process may be used for making other screw threaded blast nozzle fittings and nuts for holding flanged type nozzle casings onto nozzle fittings.

Thus a new product is provided together with apparatus and method of making which is superior to those heretofore known. The product may have a hardness of 55 to 65 Rockwell C which is so hard that it cannot be filed or machined, is very difficult and costly to grind and is highly resistant to wear. The screw threads, either external or internal, are directly cast to dimensions close enough to directly engage similarly cast screw threads on other fitting parts and the fitting is cast to dimensions close enough to engage the hardened inserts l2, without requiring any additional machining or grinding. Dry sand may be used and the screw threads may be formed directly into core sand to provide baked cores as illustrated. The threading in of a finished threaded pin into a body of sand to the desired depth and screwing it out again by reverse movement, compresses and smooths the surface of the molding sand so that these surfaces retain their form after the screw is completely withdrawn. The double screwing operation, screwing the threaded member into the mold and then out again, is superior to methods in which the threaded member is first directly molded into the sand by packing the sand around it and only screwing the member outwardly. The baking of the cores makes the fine, sharp corner screw threads less liable to break during handling and pouring. Threaded molds produced by the present method can be used to produce not only hard metal castings but also soft metal castings.

While certain novel features of the invention have been disclosed herein, and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. A blast nozzle adapted to project a stream of blast particles having severe wearing action, said nozzle comprising an outer shell made up of shell members certain of which have screw threads, said shell members being detachably connected by said screw threads, said shell having a bore with a lining of wear resisting material therein to take the direct wear of the blast particles passing through the nozzle, said shell members comprising metal castings having a hardness in as cast condition of at least Rockwell C to withstand wear due to rebound of the blast particles from the work, said shell members having their respective screw threads cast there- 2. The blast nozzle according to the preceding claim in which one of said shell members comprises a fitting for connection to the flexible hose for supplying the blast, another of said shell members comprising a nozzle casing for delivering the blast onto the work, the lining in said casing comprising a structurally weak, wear-resisting material supported by said shell.

DAVID C. TURNBU'LL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 138,277 Peet Apr. 29, 1873 992,144 Babcock May 16, 1911 1,050,370 McGlashan et al. Jan. 14, 1913 1,393,562 Matthews Oct. 11, 1921 1,398,706 Rust Nov. 29, 1921 1,477,508 Lohmann Dec. 11, 1923 1,838,417 LeMay Dec. 29, 1931 1,940,972 Schwartzkopf Dec. 26, 1933 2,369,576 Keefer Feb. 13, 1945 

